Laser processing apparatus

ABSTRACT

A laser beam irradiation unit of a laser processing apparatus includes a laser oscillator that oscillates a laser, a Y-axis scanner that executes a high-speed scan with a laser beam emitted from the laser oscillator in a Y-axis direction, an X-axis scanner that executes processing feed of the laser beam emitted from the laser oscillator in an X-axis direction, and a beam condenser. The Y-axis scanner is selected from any of an AOD, a resonant scanner, and a polygon scanner and the X-axis scanner is selected from a galvano scanner and a resonant scanner.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a laser processing apparatus includinga laser beam irradiation unit that irradiates a workpiece with a laserbeam to form a broken layer.

Description of the Related Art

There is a wafer in which a buffer layer and a light emitting layerincluding an epitaxial layer composed of an n-type semiconductor layerand a p-type semiconductor layer and plural electrodes disposed on then-type semiconductor layer and the p-type semiconductor layer arestacked by epitaxial growth over the upper surface of an epitaxysubstrate such as a sapphire substrate or a silicone carbide (SiC)substrate and plural light emitting diodes (LEDs) are formed in thislight emitting layer in such a manner as to be marked out by pluralplanned dividing lines that intersect. This wafer is divided togetherwith the epitaxy substrate along the planned dividing lines by a laserbeam or the like and individual LED chips are manufactured (for example,refer to Japanese Patent Laid-open No. 10-305420).

Furthermore, in order to improve the luminance of the LEDs and enhancethe cooling effect, the following technique has been proposed by thepresent assignee. Specifically, a transfer substrate such as amolybdenum substrate, a copper substrate, or a silicon substrate isjoined to the light emitting layer with the intermediary of a joiningmaterial (indium, palladium, or the like) to form a layer-stackingwafer. Thereafter, the buffer layer is irradiated with a laser beam fromthe epitaxy substrate side and the buffer layer is broken to form abroken layer. Then, this light emitting layer is transferred to thetransfer substrate side (refer to Japanese Patent Laid-open No.2013-21225).

SUMMARY OF THE INVENTION

By the way, in recent years, a diameter of a wafer to generate LEDs hasbeen increasing to 200 mm, 300 mm, and so forth and there has been aproblem that a throughput until individual LEDs are generated throughprocessing of the wafer lowers. It is conceivable that, in order toenhance this throughput, a spot diameter is increased to be on the orderof several millimeters, for example, when irradiation with a laser beamthat breaks a buffer layer is executed from the epitaxy substrate side.However, when the spot diameter is increased, energy of a pulse laserbeam becomes higher in proportion to an area of the spot, so that theheat dissipation rate lowers. Thus, a problem occurs that heataccumulation occurs at a laser beam irradiation position on a wafer sideand LEDs near the position irradiated with the laser beam are damaged.

Thus, an object of the present invention is to provide a laserprocessing apparatus excellent in the throughput without increasing thespot diameter of a laser beam.

In accordance with an aspect of the present invention, there is provideda laser processing apparatus including a chuck table that holds aworkpiece and includes a holding surface defined by an X-axis and aY-axis and a laser beam irradiation unit that irradiates the workpieceheld by the chuck table with a laser beam and forms a broken layer. Thelaser beam irradiation unit includes a laser oscillator that oscillatesa laser, a Y-axis scanner that executes a high-speed scan with a laserbeam emitted from the laser oscillator in a Y-axis direction, an X-axisscanner that executes processing feed of the laser beam emitted from thelaser oscillator in an X-axis direction, and a beam condenser. The spotdiameter (D) of the laser beam with which the workpiece is irradiated isset to 5 to 60 μm. The overlap rate (K) of the spot of the laser beam isset to 0.70 to 0.99. The scan speed (Vy) in the Y-axis direction is setto 1 to 300 m/s. The energy (E) of the laser beam per one pulse is setto 0.07 to 50 pJ. The repetition frequency (H) of the laser beam is setto H=Vy/{D·(1−K)} MHz. When the width of the scan by the Y-axis scanneris defined as L mm, the scan speed (Vx) in the X-axis direction is setto Vx=D·(1−K)·Vy/L mm/s. The average output power (P) of the laser beamis set to P=E·Vy/{D·(1−K)} W.

Preferably, the Y-axis scanner is selected from any of an acousto-opticdeflector (AOD), a resonant scanner, and a polygon scanner and theX-axis scanner is selected from any of a galvano scanner, a resonantscanner, and an X-axis direction feed mechanism that moves the chucktable in the X-axis direction. Preferably, the workpiece is adouble-layer substrate in which a light emitting layer is stacked overan upper surface of a sapphire substrate with the intermediary of abuffer layer and a transfer substrate is disposed to face the lightemitting layer, and the laser beam is transmitted through the sapphiresubstrate and breaks the buffer layer. Preferably, in the case in whichthe light emitting layer is stacked over the sapphire substrate, thewavelength of the laser beam is 143 nm to 266 nm.

According to the present invention, the average output power of thelaser beam that forms the broken layer is suppressed to be low, and theoccurrence of the situation in which heat accumulation occurs and damageis given to LEDs is avoided in the case of executing processing offorming the broken layer for the buffer layer that configures thedouble-layer substrate. Moreover, the time for forming the broken layerin the double-layer substrate also does not become a long time. Thus,although the spot diameter when the broken layer is formed is set small,the throughput does not lower and the light emitting layer can beefficiently transferred to the transfer substrate.

The above and other objects, features and advantages of the presentinvention and the manner of realizing them will become more apparent,and the invention itself will best be understood from a study of thefollowing description and appended claims with reference to the attacheddrawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a laser processing apparatus of anembodiment of the present invention;

FIG. 2 is a block diagram illustrating the outline of an optical systemthat configures a laser beam irradiation unit disposed in the laserprocessing apparatus illustrated in FIG. 1;

FIG. 3A is an exploded perspective view of a double-layer substrate thatconfigures a workpiece;

FIG. 3B is a partial enlarged sectional view of the double-layersubstrate illustrated in FIG. 3A;

FIG. 4A is a perspective view illustrating the form of executing laserprocessing for the double-layer substrate;

FIG. 4B is a partial enlarged sectional view of a wafer when the laserprocessing illustrated in FIG. 4A is executed;

FIG. 4C is a plan view illustrating the form of executing the laserprocessing; and

FIG. 5 is a perspective view illustrating the form of separating asapphire substrate from the double-layer substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A laser processing apparatus according to an embodiment of the presentinvention will be described in detail below with reference to theaccompanying drawings. In FIG. 1, an overall perspective view of a laserprocessing apparatus 1 of the present embodiment is illustrated. Thelaser processing apparatus 1 includes a holding unit 20 that holds aworkpiece, a movement mechanism 30 that moves the holding unit 20, analignment unit 6, a laser beam irradiation unit 8 that irradiates theworkpiece held by the holding unit 20 with a laser beam, and a displayunit 9.

The holding unit 20 includes a rectangular X-axis direction movableplate 21 placed over a base 2 movably in an X-axis direction indicatedby an arrow X in the diagram, a rectangular Y-axis direction movableplate 23 that is placed over the X-axis direction movable plate 21movably in a Y-axis direction indicated by an arrow Y in the diagram andis disposed on a pair of guide rails 22 disposed along the Y-axisdirection on the X-axis direction movable plate 21, and a holding table24 disposed on the upper surface of the Y-axis direction movable plate23. The holding table 24 is configured rotatably by rotational drivemeans that is not illustrated in the diagram. A holding surface 24 athat configures the upper surface of the holding table 24 and is definedby an X-axis and a Y-axis orthogonal to the direction of this X-axis isconfigured by a flat surface.

The movement mechanism 30 is disposed over the base 2 and includes anX-axis direction feed mechanism 32 that executes processing feed of theholding unit 20 in the X-axis direction and a Y-axis direction feedmechanism 34 that executes indexing feed of the Y-axis direction movableplate 23 in the Y-axis direction. The X-axis direction feed mechanism 32converts rotational motion of a pulse motor 35 to linear motion througha ball screw 36 and transmits the linear motion to the X-axis directionmovable plate 21 to cause the X-axis direction movable plate 21 toadvance and retreat in the X-axis direction along guide rails 2 a on thebase 2. The Y-axis direction feed mechanism 34 converts rotationalmotion of a pulse motor 37 to linear motion through a ball screw 38 andtransmits the linear motion to the Y-axis direction movable plate 23 tocause the Y-axis direction movable plate 23 to advance and retreat inthe Y-axis direction along the guide rails 22 on the X-axis directionmovable plate 21. Note that, although diagrammatic representation isomitted, position detecting means is disposed for the X-axis directionfeed mechanism 32, the Y-axis direction feed mechanism 34, and theholding table 24, the position in the X-axis direction, the position inthe Y-axis direction, and the rotational position regarding the holdingtable 24 are accurately detected and are transmitted to a control unit(diagrammatic representation is omitted) disposed in the laserprocessing apparatus 1. Then, by an instruction signal output from thiscontrol unit on the basis of the position information, the X-axisdirection feed mechanism 32, the Y-axis direction feed mechanism 34, andthe rotational drive means of the holding table 24 that is notillustrated in the diagram are driven, so that the holding table 24 canbe positioned to a desired position.

As illustrated in FIG. 1, a frame body 4 is disposed upright on alateral side of the movement mechanism 30. The frame body 4 includes avertical wall part 4 a disposed on the base 2 and a horizontal wall part4 b that extends in the horizontal direction from the upper end part ofthe vertical wall part 4 a. An optical system of the laser beamirradiation unit 8 is housed inside the horizontal wall part 4 b of theframe body 4. A beam condenser 81 included in this optical system andthe alignment unit 6 are disposed on the lower surface of the tip partof the horizontal wall part 4 b and irradiation with a laser beam fromthe beam condenser 81 is executed. The alignment unit 6 includes anilluminator that executes irradiation with a visible beam and an imagingelement (charge-coupled device (CCD)) that images the workpiece by thevisible beam. An image obtained by imaging by the alignment unit 6 issent to the control unit and is displayed on the display unit 9.

With reference to FIG. 2, the outline of the configuration of theoptical system of the laser beam irradiation unit 8 will be described.As illustrated in FIG. 2, the laser beam irradiation unit 8 includes alaser oscillator 82 that emits a pulsed laser beam LB, an attenuator 83that adjusts the output power of the laser beam LB emitted from thelaser oscillator 82, and a Y-axis scanner 84 that executes scanning(scan), at a high speed, with the laser beam LB emitted from theattenuator 83 along the Y-axis direction that defines the holdingsurface 24 a of the holding table 24. The laser beam irradiation unit 8includes also an X-axis scanner 85 that executes processing feed of thelaser beam LB in the X-axis direction that defines the holding surface24 a of the holding table 24 and the beam condenser 81 that guides thelaser beam LB that has passed through this optical system to apredetermined position on the holding table 24 perpendicularly andfocuses the laser beam LB to execute irradiation.

Note that the Y-axis scanner 84 can be selected from well-knowndeflectors and is selected as appropriate from an acousto-optic element(AOD), a resonant scanner, a polygon scanner, and so forth, for example.It suffices that the X-axis scanner 85 is means having a function ofexecuting processing feed of the laser beam LB emitted from the laseroscillator 82 in the X-axis direction that defines the holding surface24 a of the holding table 24, and the X-axis scanner 85 can be selectedfrom a galvano scanner and a resonant scanner. As described later, thespeed at which the Y-axis scanner 84 executes the scan on the holdingsurface 24 a of the holding table 24 is set higher than the speed atwhich the X-axis scanner 85 executes the scan on the holding surface 24a. Furthermore, the X-axis scanner in the present invention is notlimited to what is disposed in the optical system illustrated in FIG. 2and it is also possible to employ the X-axis direction feed mechanism 32that executes processing feed of the holding table 24 of the holdingunit 20 in the X-axis direction as the X-axis scanner in the presentinvention.

The beam condenser 81 can employ an fθ lens 81 a like one illustrated inthe diagram, for example, and condenses the laser beam LB guided to thefθ lens 81 a to irradiate the holding surface 24 a of the holding table24 with the laser beam LB perpendicularly. However, the beam condenser81 is not limited to what employs the above-described fθ lens 81 a andmay be, for example, what uses a parabolic mirror and condenses thelaser beam LB applied to a position different from the focus of theparabola that configures the parabolic mirror to emit the laser beam LBtoward the holding table 24 perpendicularly. The laser processingapparatus 1 used for the present embodiment substantially includes theconfiguration described above. Functions and operation of the laserprocessing apparatus 1 of the present embodiment will be describedbelow.

The workpiece processed by the laser processing apparatus 1 of thepresent embodiment will be described with reference to FIG. 3A and FIG.3B. FIG. 3A is an exploded perspective view illustrating the workpieceand FIG. 3B is a partial enlarged sectional view of the integratedworkpiece. As illustrated in the diagrams, the workpiece is adouble-layer substrate W composed of a wafer 10 and a transfer substrate16 disposed over a light emitting layer 11 formed over a surface of thewafer 10. In the wafer 10, a sapphire substrate 12 is employed as anepitaxy substrate. The light emitting layer 11 is stacked over thesapphire substrate 12. In the light emitting layer 11, plural lightemitting devices 14 (LEDs) configured by an epitaxial layer composed ofan n-type semiconductor layer and a p-type semiconductor layer(diagrammatic representation is omitted regarding both) formed byepitaxial growth over the sapphire substrate 12 with the intermediary ofa buffer layer 10 a and plural electrodes (diagrammatic representationis omitted) disposed on the n-type semiconductor layer and the p-typesemiconductor layer are formed in such a manner as to be marked out byplural planned dividing lines 13 that intersect. The light emittinglayer 11 is composed of gallium nitride (GaN), for example. However, thepresent invention is not limited thereto and the material of the lightemitting layer 11 can be selected from well-known semiconductors such asgallium phosphide (GaP) and indium arsenide (InAs). The buffer layer 10a is formed of the same kind of material as the above-described lightemitting layer 11. A notch 12 a that indicates the crystal orientationof the sapphire substrate 12 is formed in the wafer 10. The transfersubstrate 16 is formed of molybdenum, copper, silicon, or the like, forexample, and is disposed to face the light emitting layer 11 with theintermediary of a joining metal layer 18 selected from gold, platinum,chromium, indium, palladium, and so forth (see FIG. 3B).

The double-layer substrate W like the above-described one is prepared inadvance and is conveyed to the above-described laser processingapparatus 1. Then, as illustrated in FIG. 4A, the double-layer substrateW is placed on the holding surface 24 a of the holding table 24 in sucha manner that the side of a back surface 12 b of the sapphire substrate12 that configures the wafer 10 is oriented upward and the side of thetransfer substrate 16 is oriented downward, and is fixed by using anappropriate adhesive, wax, or the like.

Subsequently, the holding table 24 is moved in the X-axis direction andis positioned directly under the alignment unit 6. Then, imaging isexecuted from the side of the back surface 12 b of the sapphiresubstrate 12 that configures the wafer 10 and position information ofthe outer edge, the notch 12 a, and so forth of the double-layersubstrate W is detected and is stored in the control unit.

Subsequently, based on the above-described detected position informationof the double-layer substrate W, the double-layer substrate W is movedto directly under the beam condenser 81 of the laser beam irradiationunit 8 and the double-layer substrate W is positioned to a predeterminedposition. Then, as illustrated in FIG. 4B, the depth of a focal positionP of the laser beam LB with which irradiation is executed is positionedto the buffer layer 10 a formed between the sapphire substrate 12 andthe light emitting layer 11.

After the focal position P of the laser beam LB has been positioned tothe buffer layer 10 a of the double-layer substrate W in theabove-described manner, the double-layer substrate W is irradiated withthe laser beam LB and laser processing is executed. The form of theirradiation with the laser beam LB will be described more specificallybelow.

In the laser processing executed by the laser processing apparatus 1 ofthe present embodiment, as illustrated in FIG. 4C, a scan width (L)across which the scan is executed in the Y-axis direction by the Y-axisscanner 84 is set to an appropriate width (in the present embodiment, 10mm), and the X-axis scanner 85 and the Y-axis scanner 84 are actuated toposition the above-described focal position P of the laser beam LB to aleft end position A1 of a row indicated by (1). Subsequently, in thestate in which the double-layer substrate W is stopped, the laseroscillator 82 is actuated to execute irradiation with the laser beam LBand scanning is executed in the Y-axis direction by the scan width (L).Subsequently, the X-axis scanner 85 is actuated to execute processingfeed in the X-axis direction by a distance (spot diameter (D)·(1−K))that realizes an overlap rate (K) to be described later. Subsequently,the Y-axis scanner 84 is actuated again to execute scanning with thelaser beam LB in the Y-axis direction by the scan width (L) as describedabove and thereafter processing feed is executed in the X-axis directionby the distance (spot diameter (D)·(1−K)) that realizes the overlap rate(K) to be described later again. The operation of the X-axis scanner 85at this time is intermittent operation in which stop and actuation arerepeated.

By repeating such scanning, as illustrated in FIG. 4C, the irradiationwith the laser beam LB is executed across the whole of the first row (1)in the X-axis direction and a broken layer 100 is formed in the bufferlayer 10 a (see FIG. 4B). After the broken layer 100 has been formed asdescribed above in the first row (1) of the double-layer substrate W,the Y-axis scanner 84 and the X-axis scanner 85 are actuated to positionthe focal position P of the laser beam LB to a left end position A2 of arow (2). Then, the broken layer 100 is formed across the whole region ofthe row (2) similarly to the above-described row (1). Similarly, alsofor a row (3) and a row (4), the above-described laser processing isexecuted in such a manner that left end positions A3 and A4 are employedas the processing start positions. Moreover, this is executed across thewhole region in the Y-axis direction and the broken layer 100 is formedfor the buffer layer 10 a of the whole region of the double-layersubstrate W.

After the broken layer 100 has been formed as described above, thesapphire substrate 12 is separated from the double-layer substrate W asillustrated in FIG. 5. Thereby, the light emitting layer 11 istransferred from the sapphire substrate 12 to the transfer substrate 16.Note that the sapphire substrate 12 separated from the double-layersubstrate W is subjected to polishing and cleaning treatment and isreused.

It is important that the above-described laser processing of the presentembodiment be executed in such a manner that setting is made to satisfythe following conditions.

Spot diameter (D): 5 to 60 μm

Spot overlap rate (K): 0.70 to 0.99 (70% to 99%)

Y-axis direction scan speed (Vy): 1 to 300 m/s

Energy (E) per one pulse: 0.07 to 50 μJ

In the present embodiment, specifically, laser processing conditions areset as follows.

Spot diameter (D): 10 μm

Spot overlap rate (K): 0.90 (90%)

Y-axis direction scan speed (Vy): 50 m/s

Energy (E) per one pulse: 1 μJ

Y-axis direction scan width (L): 10 mm

In the present embodiment, as described above, the sapphire substrate 12is selected as the epitaxy substrate that configures the wafer 10. Thus,the wavelength of the laser beam LB oscillated by the laser oscillator82 is set to such a wavelength as to be transmitted through the sapphiresubstrate 12 (143 to 266 nm). However, the present invention is notlimited thereto and well-known another substrate (for example, SiCsubstrate) can be selected as the epitaxy substrate. In this case,irradiation with a laser beam with such a wavelength as to betransmitted through the selected material is executed.

In addition to being set to the above-described processing conditions,the laser processing apparatus 1 of the present embodiment is set tosatisfy the following condition expressions regarding the repetitionfrequency (H) of the laser beam, the scan speed (Vx) in the X-axisdirection, and the average output power (P) of the laser beam LB.

H=Vy/{D·(1−K)} MHz

Vx=D·(1−K)·Vy/L mm/s

P=E·Vy/{D·(1−K)} W

That is, in the present embodiment, these parameters have the followingvalues.

Repetition frequency (H)=50/{10·(1−0.90)}=50 MHz

X-axis direction scan speed (Vx)=10·(1−0.90)·50/10=5 mm/s

Average output power (P)=1.50/{10·(1−0.90)}=50 W

Thus, the time to process a wafer with a diameter of 200 mm as describedabove is calculated as follows.

Processing time (T)=(200/5)·(200/10)·(3.14/4)=628 seconds (=10 minutes28 seconds)

As described above, according to the present embodiment, the averageoutput power (P) is suppressed to be comparatively low. Thus, even whenthe processing of forming the broken layer 100 is executed for the wholeregion of the double-layer substrate W, the occurrence of the situationin which heat accumulation occurs and damage is given to LEDs isavoided. Moreover, the time for forming the broken layer 100 in thewhole region of the double-layer substrate W also does not become a longtime. Thus, although the spot diameter (D) is set small, the throughputdoes not lower and the light emitting layer 11 can be efficientlytransferred from the sapphire substrate 12 to the transfer substrate 16.

The present invention is not limited to the details of the abovedescribed preferred embodiment. The scope of the invention is defined bythe appended claims and all changes and modifications as fall within theequivalence of the scope of the claims are therefore to be embraced bythe invention.

What is claimed is:
 1. A laser processing apparatus comprising: a chucktable that holds a workpiece and includes a holding surface defined byan X-axis and a Y-axis; and a laser beam irradiation unit thatirradiates the workpiece held by the chuck table with a laser beam andforms a broken layer, wherein the laser beam irradiation unit includes alaser oscillator that oscillates a laser, a Y-axis scanner that executesa high-speed scan with a laser beam emitted from the laser oscillator ina Y-axis direction, an X-axis scanner that executes processing feed ofthe laser beam emitted from the laser oscillator in an X-axis direction,and a beam condenser, a spot diameter (D) of the laser beam with whichthe workpiece is irradiated is set to 5 to 60 μm, an overlap rate (K) ofa spot of the laser beam is set to 0.70 to 0.99, a scan speed (Vy) inthe Y-axis direction is set to 1 to 300 m/s, and energy (E) of the laserbeam per one pulse is set to 0.07 to 50 μJ, repetition frequency (H) ofthe laser beam is set toH=Vy/{D·(1−K)} MHz, when a width of the scan by the Y-axis scanner isdefined as L mm, a scan speed (Vx) in the X-axis direction is set toVx=D·(1−K)·Vy/L mm/s, and average output power (P) of the laser beam isset toP=E·Vy/{D·(1−K)} W.
 2. The laser processing apparatus according to claim1, wherein the Y-axis scanner is selected from a group consisting of anacousto-optic deflector, a resonant scanner, and a polygon scanner andthe X-axis scanner is selected from a group consisting of a galvanoscanner, a resonant scanner, and an X-axis direction feed mechanism thatmoves the chuck table in the X-axis direction.
 3. The laser processingapparatus according to claim 1, wherein the workpiece is a double-layersubstrate in which a light emitting layer is stacked over an uppersurface of a sapphire substrate with intermediary of a buffer layer anda transfer substrate is disposed to face the light emitting layer, andthe laser beam is transmitted through the sapphire substrate and breaksthe buffer layer.
 4. The laser processing apparatus according to claim3, wherein a wavelength of the laser beam is 143 to 266 nm.